1,260 research outputs found
Paintings and their implicit presuppositions: High Renaissance and Mannerism
All art historians who are interested in questions of "styles" or "schools" agree in identifying a High Renaissance school of Italian
painting. There is, however, a disagreement, which has seemed nonterminating, regarding Mannerism: Is it another distinct school or
is it merely a late development of the Renaissance school? We believe that this disagreement can be terminated by distinguishing questions of
fact about paintings from questions about the definitions of schools. To this end we have had two representative subsets of paintings--one
earlier, one later--rated on four of the dimensions of implicit presuppositions that we have introduced in other Working Papers. When
the paintings are scaled in this way a very distinct profile emerges for the earlier, or Renaissance, paintings. In contrast, the later, or
Mannerist, paintings are so heterogeneous that we conclude that they are best described as deviations from the Renaissance profile, rather
than a separate school. These results are not unimportant--at least for art historians. But they are more important methodologically
inasmuch as the procedures applied here can be used in classifying and distinguishing from one another all kind of cultural products
Paintings and their implicit presuppositions : a preliminary report
In a series of earlier papers (Social Science Working Papers 350, 355. 357) we have studied the ways in which differences in "implicit presupposi tions" (i. e •• differences in world views) cause scientists and historians to reach differing conclusions from a consideration of the same evidence. In this paper we show that paintings are characterized by implicit presuppositions similar to those that characterize the written materials -- essays, letters, scientific papers -- we have already studied
Woody species and forest structure in northern Missouri riparian forests with different ages and watershed sites
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file.Title from title screen of research.pdf file (viewed on May 1, 2009)Vita.Thesis (Ph.D.) University of Missouri-Columbia 2006.A chronosequence (1 to 250+ years) of 160 woody species plots was established throughout northern Missouri riparian forests to explain the influence of site hydrology and stand age on species distribution and forest structure. Stand age was found to be the dominant factor affecting species distribution and forest structure across the chronosequence. Watershed size was found to influence only species distribution; forest structure (tree height, coarse woody debris, size and age distributions) was not affected by watershed size. There were seven significant trends in the tree-watershed data: 1) very flood tolerant species importance values increased in larger watersheds; 2) shade tolerance was the dominant mechanism structuring riparian communities; 3) watershed size influenced species distribution; 4) early successional species differed among watershed sizes; 5) species richness decreased with increasing watershed size; 6) mortality rates were fairly uniform among watershed sizes; and 7) forest structure was not influenced by watershed size. In the incised alluvial channels of northern Missouri, the increases in flood tolerance, decreases in species richness, and the lack of influence on forest structure could be the result of groundwater dynamics or less habitat heterogeneity in larger watersheds rather than differences in flood duration; in addition, flooding interacts with seedling germination and patch size to create highly diverse forests.Includes bibliographical reference
Microwave cavity-enhanced transduction for plug and play nanomechanics at room temperature
Nanomechanical resonators with increasingly high quality factors are enabled
following recent insights into energy storage and loss mechanisms in
nanoelectromechanical systems (NEMS). Consequently, efficient, non-dissipative
transduction schemes are required to avoid the dominating influence of coupling
losses. We present an integrated NEMS transducer based on a microwave cavity
dielectrically coupled to an array of doubly-clamped pre-stressed silicon
nitride beam resonators. This cavity-enhanced detection scheme allows resolving
the resonators' Brownian motion at room temperature while preserving their high
mechanical quality factor of 290,000 at 6.6 MHz. Furthermore, our approach
constitutes an "opto"mechanical system in which backaction effects of the
microwave field are employed to alter the effective damping of the resonators.
In particular, cavity-pumped self-oscillation yields a linewidth of only 5 Hz.
Thereby, an adjustement-free, all-integrated and self-driven
nanoelectromechanical resonator array interfaced by just two microwave
connectors is realised, potentially useful for applications in sensing and
signal processing
Finite time St\"uckelberg interferometry with nanomechanical modes
St\"uckelberg interferometry describes the interference of two strongly
coupled modes during a double passage through an avoided energy level crossing.
In this work, we experimentally investigate finite time effects in
St\"uckelberg interference and provide an exact analytical solution of the
St\"uckelberg problem. Approximating this solution in distinct limits reveals
uncharted parameter regimes of St\"uckelberg interferometry. Experimentally, we
study these regimes using a purely classical, strongly coupled nanomechanical
two-mode system of high quality factor. The classical two-mode system consists
of the in-plane and out-of-plane fundamental flexural mode of a high stress
silicon nitride string resonator, coupled via electric gradient fields. The
dielectric control and microwave cavity enhanced universal transduction of the
nanoelectromechanical system allows for the experimental access to all
theoretically predicted St\"uckelberg parameter regimes. We exploit our
experimental and theoretical findings by studying the onset of St\"uckelberg
interference in dependence of the characteristic system control parameters and
obtain characteristic excitation oscillations between the two modes even
without the explicit need of traversing the avoided crossing. The presented
theory is not limited to classical mechanical two-mode systems but can be
applied to every strongly coupled (quantum) two-level system, for example a
spin-1/2 system or superconducting qubit
Coherent control of a nanomechanical two-level system
The Bloch sphere is a generic picture describing a coupled two-level system
and the coherent dynamics of its superposition states under control of
electromagnetic fields. It is commonly employed to visualise a broad variety of
phenomena ranging from spin ensembles and atoms to quantum dots and
superconducting circuits. The underlying Bloch equations describe the state
evolution of the two-level system and allow characterising both energy and
phase relaxation processes in a simple yet powerful manner.
Here we demonstrate the realisation of a nanomechanical two-level system
which is driven by radio frequency signals. It allows to extend the above Bloch
sphere formalism to nanoelectromechanical systems. Our realisation is based on
the two orthogonal fundamental flexural modes of a high quality factor
nanostring resonator which are strongly coupled by a dielectric gradient field.
Full Bloch sphere control is demonstrated via Rabi, Ramsey and Hahn echo
experiments. This allows manipulating the classical superposition state of the
coupled modes in amplitude and phase and enables deep insight into the
decoherence mechanisms of nanomechanical systems. We have determined the energy
relaxation time T1 and phase relaxation times T2 and T2*, and find them all to
be equal. This not only indicates that energy relaxation is the dominating
source of decoherence, but also demonstrates that reversible dephasing
processes are negligible in such collective mechanical modes. We thus conclude
that not only T1 but also T2 can be increased by engineering larger mechanical
quality factors. After a series of ground-breaking experiments on ground state
cooling and non-classical signatures of nanomechanical resonators in recent
years, this is of particular interest in the context of quantum information
processing
Some Implicit Presuppositions of Typical Writings in the Field of American Intellectual History
This paper reports a study made of some of the implicit presuppositions contained in the following materials: The Federalist, papers 10 and 51 by Madison, selections from de Tocqueville's Democracy in America; Emerson's "The American Scholar"; Melville's "Bartleby the Scrivener"; "Washington as Commander in Chief” in Bancroft's History of the United States; and "A Small Group of Men Hold in their hands the Business of this Country," a Senate speech by Robert M. LaFollette, Fifteen students at the Claremont Graduate School, who had taken a course in which these materials were studied, rated them on seven scales, or "dimensions, " each of which represents one of a contrasting pair of implicit presuppositions which we have identified and defined. At 19 of the 42 choice points at which decisions had to be made (six selections on seven dimensions) the ratings proved to be significant at p < .05 level. These results thus expand the "scope" of our set of implicit presuppositions to include new materials not previously investigated. In short, it has been shown that readers who are guided by our definitions are able to agree on some of the implicit assumptions contained in a representative sample of writings in the field of American intellectual history
Some Implicit Presuppositions Involved in the Disagreement over the DNA Guidelines
This paper is one of a series reporting studies we have made of differences in implicit presuppositions and of how such differences affect the ways people reason. In the study reported here 26 students (14 at Caltech; 12 at Claremont) read and rated four letters which had appeared in the correspondence columns of Science. Two of the letters defended the guidelines governing DNA research; two criticized them. The students rated the letters on six scales, or "dimensions," each of which represents a contrasting pair of implicit presuppositions, which we have identified and defined. For two of the six dimensions all four of the letters were rated in the predicted direction, and all are statistically significant. On a third dimension all four of the letters were rated in the predicted direction, but only three of the four are statistically significant. For the other three dimensions there was no consistent pattern, though some of the results on some of the dimensions were in the predicted direction and are statistically significant. Thus this study shows that in certain important respects the presuppositions of the proponents and the presupposition of the opponents of the guidelines are not only different but diametrically opposed
Signatures of two-level defects in the temperature-dependent damping of nanomechanical silicon nitride resonators
The damping rates of high quality factor nanomechanical resonators are well
beyond intrinsic limits. Here, we explore the underlying microscopic loss
mechanisms by investigating the temperature-dependent damping of the
fundamental and third harmonic transverse flexural mode of a doubly clamped
silicon nitride string. It exhibits characteristic maxima reminiscent of
two-level defects typical for amorphous materials. Coupling to those defects
relaxes the momentum selection rules, allowing energy transfer from discrete
long wavelength resonator modes to the high frequency phonon environment
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